Update the \X documentation to reflect the new behaviour in PCRE ≥ 8.32.

Fixes doc bug #65651 (Since PCRE 8.32, \X does not match (?>\PM\pM*)).


git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@331343 c90b9560-bf6c-de11-be94-00142212c4b1